CVE-2026-34877: Arm Mbed TLS

Critical severity, CVSS 9.8. EPSS: 0.7% chance of exploitation in the next 30 days.

An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.

Affected products

• Arm Mbed TLS: from 2.19.0, before 3.6.6 (fixed in 3.6.6)
• Trustedfirmware Mbed TLS: version 4.0.0 only

Published 2026-04-02. Last modified 2026-07-24.